16oz Rimmed Northern Night Mug #N2974The dramatic "Northern Night" surface is achieved by combining two quite different glazes. The darker base is an oil spot glaze which when fired quickly to a high heat, causes iron components to burst to the surface and leave glistening or sparkling highlights. Layered on this is the blue crystalline glaze, which creates a luminescent Northern Lights effect when it melds in the kiln with the darker glaze.